Heat hardening synthetic resins



8, 1937. F. I. BENNETT, JR 2 HEAT HARDENING SYNTHETIC RESINS Filed Nov. 15,1954

Patented. June 8, 193.7

PATENT OFFICE HEAT HARDENING SYNTHETIC ansms Frank I. Bennett, JrQHighland Park, N. J.,' as

signon to The Revolite Corporation, New Brunswick, N. J., a corporation of New Jersey Application November 15, 1934, Serial No. 753,231

2 Claims.

The invention relates to a method of heat hardening synthetic resins, and it comprises passing a fllmiform layer of a condensable synthetic resin on a cellulosic fabric, as paper or 5 cloth, through an oven or' chamber heated to a temperature substantially inv excess of the scorching point of cellulose at a transitional velocity such that effective polymerization and/or condensation ofthe synthetic resin is accoml0 plished while scorching or charring of the cellulosic base is avoided;' and, when the said resin has been applied to the said base in a solvent vehicle, sometimes but not always, though preferably, first passing the fabric-borne resin through a low temperature drying chamber whereby the solvent is removed before the said resin is admitted to the high temperature oven; all as more fully hereinafter described and claimed.

Resins of the heat hardening type may be 'flnally hardened by condensation and/or polymerization 'over a fairly wide range of temperatures above that critical temperature at which polymerization starts. The time necessary to ef- 5 feet substantially complete final hardening is roughly inversely proportional to the temperature; thus, as is well known, relatively high temperatures for short times produce the same hardening effect as lower temperatures for longer times. In resinous bodies of appreciable mass the heat conductivity of the mass is a limiting factor, but when the resinous mass is but a filmiform layer, as a suxface coating on a fabric web as paper or cloth or even as an impregnant coextensive therewith, the surfacemass ratio is so high that heat conductivity. is not of primary importance.

Heretofore, it has been customary to'heat harden condensable synthetic resins, when 40 coated on or permeating fabrics, by subjecting the composite to heat supplied at a sufliciently low temperature to avoid scorching or charring the cellulosic material of the base fabric however long may be the heating required to effect the desired final condensation; Moreover, it-has been customary to evaporate the solvent in the same chamber in which the final hardening is produced. Inasmuch as these coated or impregnated products are customarily handled from long rolls, the process is progressively continuous and the rate of linear production is limited by the size of the oven and the time required for final hardening at the relatively low temperatures required for safety in view of the inflammability of the resin solvents and imposed by the necessity of the avoidance of scorching or charring the cellulosic component of the fabric base.

It isan object of this invention to provide a process whereby the solvent vehicle, when such has been used, is removed by a preliminary drying in a relatively low temperature drying oven provided with effective exhaust means; and, in any event, whereby the coated or impregnated material is passed through an oven, supplied with heating elements. and adapted to maintain a temperature substantially in excess of the charring point of the cellulosic component of the fabric, at'such a rate that charring is avoided while the desired hardening of the resin is accomplished. It is another object of this invention to provide a process wherein the hazards of solvent removal are segregated from those incident to the use of high temperatures efflcient for rapid hardening a: the resin. It is another object of the process of this invention to permit the use of heating chambers very small as compared to those required to heat harden resin coated or impregnated fabrics at the prior low temperatures and at comparable linear rates of production.

The process of the invention is based on the discovery that the heat characteristics of condensable synthetic resins are such that, when coated on or permeating cellulosic fabrics, substantially complete final polymerization or hardening of the resin is obtainable without detriment to the supporting fabric, at temperatures and in such times as would cause a scorching or other detriment of the cellulosic fabric in the absence of, the consociated resin. Why this should be thus I do not profess to know but merely state my observation of fact that a cloth fabric carrying as little as one ounce of condensable synthetic 'resin per square yard or as much as eight ounces per square yard may be heat hardened at temperatures between 350 F. and 550 F. at a linear velocity of between and 3 feet per minute per foot of oven length; and that such transitional velocity at these temperatures would cause a' perceptible darkening or scorching of the cellulosic material under like conditions but in the absence of the consociated resin.

As stated, when solvents have been used and are retained in the body of the coating or permeating synthetic resin, I prefer to pass thecomposite of fabric and resin through a low temperature oven of any conventional design capable of effectively evaporating the solvent and fromwhichthe'samemayberemovedasfastas evaporated by exhaust means either to the open air or to appropriate solvent recovery condeming means.

hr the final heathardening I prefer to use an oven comprising horizontally distributing heating elements, which may be and preferably are electrically energised, over which the fabric maybedrawninoroutofcontacttherewithas may be expedient in any given case. This oven may be of any conventional type adapted to provide for such recirculation of theheated air as to avoid saturation thereof by the vaporiaed products of condensation and therefore the ob- ,iectionable precipitation ofthese products within the heating chamber proper. vAs oven structures of widely variant typemay be satisfactorily used for practicing my process and as I do not consider such structures to be part of this invention, no further description thereof is here deemed necl'ior clarity of presentation, however, reference is had to the schematic drawing, in which A is a'roll of fabric to be coated or impregnated;

B is a schematic representation of a knife spreader. A calender or other coating or impregnating device may be substituted for the knife spreader shown as may be'required by the character of the product.

'0 is a low temperature oven provided with steam coils I and exhaust pipes 2 leading to an exhaust fan manifold l. The exhaust fan, not

shown, may, as stated, exhaust the inflammable solvent vapors to the open air or to any suitable condensing means.

D is a diagrammatic representation'of a fire barrier which may be and conveniently is a slot in the fire wall. The exhaust fan referred to as acting on the exhaust manifold 3 produces a low pressure in the low temperature oven chamber and, hence, given appropriate closures for this chamber, produces an influx of air through the slot 4 in the fire barrier D countercurrent to the transitional motion of the fabric through the slot in said fire barrier.

aosasas Ilsa w creprescntationofahish temperature oven provided preferably with electrical heating units I and a hood 0 provided with exhaust outlets I.through which a small amount ofairmaybewithdrawnatsucharateasto prevent saturation of the air within the hood by the products of condensation.

1'. is a representation of a reel adapted to receive and wind the finished product.

By the expression "scorching", as used herein, is meant a visually discernible discoloration produced by heat.

. By the expression .detriment to the fabric". as usedherein, is meant .the inclusion of such detrimental change as loss of'strength for instance.

By the term "fabricf. as used herein, is meant any cellulosic sheet material whether in the form of paper, woven fabric, or homogeneous sheet material producedfrom cellulose derivatives.

Having described the invention. 1 claim:- 1. Apparatus for heat hardening a heat hardenable fllmiformsurface coating which comprises in combination, supply and wind-up rolls, a preheater, and an oven intermediate said rolls and constructed and arranged for the passing of the coated web from the supply roll to the wind-up roll, and a baiiie intermediate the pre-heater and the oven and constituting a fire barrier. said bailie having a slit forming a passway for the web.

2. Apparatus for heat hardening a. heat hardenable filmiform surface coating which comprises, in combination, supply and wind-up rolls, a preheater equipped with an exhaust manifold and eflective to remove solvents, a relatively higher FRANK I. BENNETT, Jl. 

